A flat-panel CRT display basically consists of an electron-emitting device and a light-emitting device that operate at low internal pressure. The electron-emitting device, commonly referred to as a cathode, contains electron-emissive elements that emit electrons over a wide area.
The emitted electrons are directed towards light-emissive elements distributed over a corresponding area in the light-emitting device. Upon being struck by the electrons, the light-emissive elements emit light that produces an image on the viewing surface of the display.
When the electron-emitting device operates according to field-emission principles, electrically conductive seed material is commonly placed in series with the electron-emissive elements to gate the magnitude of current flow through the electron-emissive elements. FIG. 1 illustrates a conventional field-emission device, that so utilizes the seed material.
In the field emitter of FIG. 1, electrically seed (catalyst) layer 25 overlies emitter electrodes 15 provided on baseplate 10. Gate (or gate) electrodes 40, one of which is depicted in FIG. 1, are situated on dielectric layer 35 and passivation layer 30 situated on the gate layer 40 and cross over emitter electrodes 15. Electron-emissive elements 45 are situated on emitter conductive layer 25 in openings 50 through dielectric layer 35 and are exposed through corresponding openings 50 in gate electrodes 40.
Seed layer 25 is typically a blanket layer. That is, seed layer 25 extends in a continuous manner over the emitter electrodes 15 and the intervening portions of baseplate 10. Consequently, each electron-emissive elements 45 is electrically coupled through seed layer 25 to each other element 45. In the prior art device shown in FIG. 1, the electron emissive elements are a group carbon based filaments.
The catalyst layer 25 is normally a conductive material that is layer 25 effectively does not electrically isolate each group of elements 45 from each other. Thus, there could be a kind of intercoupling of electrons emissive elements 45 through layer 25. That means electron emission from a group of elements 45 would have an effect on the other group of element 45. A degradation of one group of elements 45 usually means other groups of elements 45 would have an effect on the emitting of other groups of element 45.
The intercoupling of the electron emission elements 45 also causes an undesirable process of non-uniformity of deposition, patterning and etching of the electron emission elements 45. The differences in the uniformity of the electron emission elements creates a situation where the elements 45 have different threshold voltage for electron emission. Thus, most of elements 45 would not start to emit electrons at the same time.
Because of the intercoupling provided by catalyst layer 25, a few of the groups of the elements 45 that would have low value of voltage could become the primary source of electron emitting for the entire group in the display device rather than emitting electrons from most of the groups of elements 45. Thus, those elements 45 that act as a primary electron emitting source could result in the emitter degradation.
It is therefore desirable to have a seed layer upon which the carbon based emitter electrons can be formed and treated that reduces the number and/or complexities of steps conventionally required to fabricate the field emitter structure.
It is desirable to have a conductive seed layer that provides conductivity at selected areas along baseplate 10 but does not itself electrically interconnect these areas. In this regard, electron-emissive elements 45 at each location where one gate electrode 40 crosses over one emitter electrode 15 operate as a unit and need not be conductively coupled.
It is also desirable to configure the seed layer in such a way that underlying emitter electrodes be externally electrically accessible along their upper surfaces without the necessity of performing a separate etching operation to cut openings through the seed layer. Furthermore, it is preferable to provide a suitable pattern in the seed layer without employing any additional masking steps beyond those used for patterning other components in the field emitter.